The present invention relates to the production of soap bar bases, particularly those comprising alkali metal or ammonium alkanoyl isethionate in the final bar.
Typically, the production of the alkanoyl isethionate used in the bars results from the reaction of (1) fatty acids (typically predominantly C12-C14 fatty acids such as coconut oils or palm kernel acids which are used in the reaction) and (2) alkali metal or ammonium isethionate (e.g., sodium isethionate, HOCH2CH2SO3Na).
The direct esterification of fatty acid and isethionate results in the production, depending on the rate of conversion, of directly esterified fatty acyl isethionate (DEFI). In a typical DEFI reaction, for example, coconut fatty acid may be reacted with sodium isethionate (e.g., at ratio of greater than 1:1) and reaction mixture are then pumped to a “stripper” reactor. In the stripper reactor, typically some of the shorter chain fatty acids are “stripped” (and recycled to the first reactor), while some longer chain fatty acids (e.g., C16-C20 fatty acids such as, for example, stearic acid) are added. While not wishing to be bound by theory, it is believed that the longer chain fatty acids help both to ensure there is a proper ratio of long to short chain fatty acids in the final bar such that acceptable lather values are obtained (e.g., at least 80 ml lather volume), as well as to minimize regions of sodium stearate formation which can account for grittiness.
Although the resultant DEFI solution (i.e., solution comprising converted DEFI and unconverted fatty acids and isethionates) produced in a typical “stripper” reaction is adequate, it would be a substantial benefit to eliminate the “stripper” step because it would result in an entire process step which would not be required. The savings in equipment costs and maintenance, space savings etc. would result in tremendous efficiencies and potentially millions of dollars worth of savings. Thus, applicants have long considered it a desirable goal to find a way to so eliminate the strip step in a so-called “no-strip” process.
There thus seems to be a need to find a way to remove excess free fatty acid (e.g., previously done by a “stripper” process) since providing a larger excess of fatty acid leads to softer, difficult to process bars.
Unexpectedly, applicants have found that, when the reactants are combined as has been previously done to provide DEFI solution (resulting in DEFI, and unreacted fatty acids and isethionate), if, rather than strip away the typically shorter chain fatty acids and add longer chain fatty acid at the stripping stage, the hot DEFI solution is quenched and neutralized (e.g., by addition of sodium hydroxide solution), and the fatty acids are converted to soap in situ. This neutralization both reduces the level of foam-suppressing fatty acid (more soap, less fatty acid), and further allows the soap to be used with the bar base rather than have to add soap in a different step.